1. Field of the Invention
The present invention relates to a method of transferring a sample to and from a treating chamber such as a charged beam drawing apparatus kept in a vacuum atmosphere through a pressure-regulative preparatory chamber, an apparatus for supporting the practice of the sample transferring method, a charged beam drawing apparatus and a charged beam drawing method.
2. Related Art
In the process for manufacturing a semiconductor device, as well known in the art, there is employed the lithography technique by which a mask pattern drawn on a mask made of quartz is transferred to a wafer. For forming the mask pattern on the mask, there is generally employed a charged beam drawing apparatus. In this charged beam drawing apparatus, an electron beam, as emitted from an electron gun as the charged beam, is shaped and reduced to a desired shape, so that this shaped electron beam is repeatedly deflected and irradiated according to pattern data to form the pattern on the mask.
In recent years, the high degree of integration of the semiconductor device has progressed so rapidly that the mask pattern to be used in the lithography has become finer and finer. As the pattern size is thus reduced to dense the pattern, there increases the pattern data necessary for forming the mask pattern. This raises a tendency to deteriorate the throughput of the charged beam drawing apparatus. In order to prevent this deterioration in the throughput, it is conceivable to improve the performance of the charged beam drawing apparatus, but this improvement is not easy in the least. In this place, therefore, endeavors have been devoted to an improvement in the production yield of masks. This is the concept of retaining the throughput of the entire mask production system by increasing the conforming masks having less pattern defects.
The defects of mask patterns are frequently caused by the sticking of particles despite of various causes. When a mask is to be drawn by the charged beam drawing apparatus, more specifically, the particle or the like will form an unexposed portion to cause the pattern defect if it shields the charged beam at such a portion of a mask substrate having an applied photosensitive resist as to be exposed. Here, it has been performed to correct the formed pattern on the basis of the information which is acquired by locating the defects and by examining the number of defects by means of a defect inspection system. For many pattern defects, however, it takes a long time to correct the defects and to inspect them again. Thus, such defective devices are disposed.
In order to improve the production yield of masks effectively, therefore, it is necessary to establish a technique or method to keep the portion to be exposed away from the particle such as dust for the time period from the application of the photosensitive resist to the mask substrate to the drawing action with the charged beam.
The particle can be exemplified by the dust floating in the air, an organic substance such as the skin of an operator handling the mask, or metal powder to come from the sliding portions of the apparatus.
In the mask production site of the prior art, therefore, the degree of cleanness of the clean room, in which the mask manufacturing apparatus is installed, is improved from the class 100 (100 particles of 0.3 .mu.m per cubic meters) to the class 10 (10 dusts of 0.3 .mu.m per cubic meters). On the other hand, the mask having an applied photosensitive resist is tested by an atmospheric dust tester to confirm that no particle is on the mask surface. Before the mask is set in the drawing apparatus, moreover, a visual inspection test is performed to confirm the absence of an atmospheric dust by irradiating the mask drawing surface with an oblique illumination.
In recent years, there has been desired the appearance of a semiconductor device matching 1G (giga) DRAM. In this semiconductor device having an extremely high degree of integration, the width of the pattern to be drawn on the wafer is 0.15 .mu.m or less. At the actual transfer of the mask pattern to the wafer, moreover, there is adopted a method of transferring the mask pattern by reducing it to one quarter. It is, therefore, anticipated that the size of the necessary mask pattern is 0.6 .mu.m or less.
When the pattern of such size is to be drawn on the mask, an environment for a clean room having a degree of cleanness of the class 10 (10 dusts of 0.3 .mu.m per cubic meters) is insufficient, and the clean room has to have a cleanness from the class 1 (1 dusts of 0.3 .mu.m per cubic meters) to the class 0.1 (0.1 dusts of 0.3 .mu.m per cubic meters).
However, the realization of such environment for the entire clean room is accompanied by technical and economic difficulties. It is, therefore, conceivable to eliminate the technical and economic difficulties not by improving the entire cleanness of the clean room but by keeping only the minimum target environment clean. By using an atmospheric dust tester of higher sensitivity and accuracy, moreover, the works of the visual inspection tests requiring the manpower can be eliminated to reduce the possibility for the atmospheric dust to stick to the mask.
However, the charged beam drawing apparatus such as an electron beam drawing apparatus for masks or a direct electron beam drawing apparatus is equipped with a preparatory chamber, in which the vacuum and the atmosphere are repeated, so as to draw a pattern on the mask in the vacuum atmosphere. In order to eliminate the vibrations coming from the outside, moreover, the charged beam drawing apparatus is isolated from the building by a vibration proofing device. This makes it difficult to locally clean the space between the preparatory chamber and the outside mask transfer aparatus, and the atmospheric dust may stick to the drawing face of the mask having the applied photosensitive resist while the mask is being transferred from the outside mask transfer apparatus to the preparatory chamber. Moreover, the atmospheric dust may migrate during the transfer of the mask to the preparatory chamber and may float during the evacuation of the preparatory chamber and stick to the drawing face of the mask.
Against the contamination of the particle sticking to the surface of the sample, as well known in the art, remarkable considerations have been taken in the prior art. However, the allowable size of particle grows smaller and smaller for the narrower circuit lines so that the contamination cannot be avoided by the conventional system or by the cares of the operator.
As described hereinbefore, a mask of high quality is indispensable for realizing the semiconductor device corresponding to 1G DRAM. For this high quality, the mask has to be handled in a cleaner atmosphere. In this case, it is desirable not to improve the degree of cleanness of the entire clean room but to adopt the so-called "local cleaning method" by which only the minimum environment, as required, is kept clean. Since the charged beam drawing apparatus to be used for drawing the pattern on the mask is equipped with the preparatory chamber repeating the vacuum and the atmosphere, however, there arises the problem that it is difficult to locally clean the space between the preparatory chamber and the mask supply/recovery device.